[quote]What's the Dungeon look like from the outside?[/quote]
A mountain fortress would be the most effective. Gives us the high ground to spot any enemies that might come at us an mass. Thus only smaller groups of adventurers would be able to approach unnoticed, which will be easier to deal with.

[quote]Structure: What are the rules and floors made of?[/quote]
Stone probably? I mean if we can get something fancier like some cool black rocks and iron I won't be against it. Probably whatever isn't too flammable. 

[quote]Lighting: What lights the Dungeon and how dark is it?[/quote]
Magic lights are usually pretty good. Mainly so we can turn it off when mortals come and cut visibility. Not sure how many of us have some form of darkvision, but every advantage we can get in our fortress is better.

[quote]Atmospherics: What sounds and smells greet those who enter.[/quote]
For a fortress, probably a mountain breeze scent. Alternatively a very strong, almost wretched stench that may sicken mortals with weaker constitution and foul up scent based detection. 

[quote]Hoard: What makes up the piles of treasure in your hoard?[/quote]
Gold would probably be the easiest. Either that or weapons. Trade in steel or gold for goods and services.